1. Field of the Invention
The present invention relates to a liquid crystal display apparatus.
2. Description of Related Art
A liquid crystal display apparatus is used as a monitor of a personal computer (PC), a personal digital assistant device and the like, or a display apparatus of a TV, taking advantages of its low power consumption or reduced size and light weight. A liquid crystal display apparatus includes a plurality of pixels arranged in matrix, and displays images by performing light modulation for each pixel.
An active matrix type liquid crystal display apparatus using a thin film transistor (TFT) as a switching element is widely used as a liquid crystal display apparatus.
Japanese Unexamined Patent Application Publication No. 2004-312780 (patent document 1) and Japanese Unexamined Patent Application Publication No. 2008-8934 (patent document 2) each disclose a liquid crystal display apparatus of parallax barrier system with multi screen that includes a parallax barrier layer in a viewing side of a liquid crystal panel and is capable of displaying different images at the same time to a plurality of observers in different visual directions by one liquid crystal display apparatus.
Referring to FIG. 13, a basic configuration of a TFT liquid crystal display apparatus of conventional parallax barrier system is described. FIG. 13 shows a schematic cross sectional view. This example will be described taking a right and left two-screen display as an example that displays different images to observers in the left side and the right side with respect to the display screen.
A liquid crystal display apparatus 3 shown in FIG. 13 includes a liquid crystal panel 4 in which a TFT substrate 204 and an opposed substrate (CF substrate) 206 are bonded to each other with a liquid crystal layer 205 interposed therebetween. The TFT substrate 204 includes a pixel electrode (not shown) and a TFT (not shown) formed for each pixel. The TFT substrate 204 further includes a plurality of signal lines 210 including a plurality of gate lines (scan signal lines) and a plurality of source lines (display signal lines) to drive the display apparatus at each pixel, and a plurality of lead-out lines (not shown) connected to the plurality of signal lines 210. The opposed substrate 206 includes an opposed electrode (common electrode), a colored layer (color filter layer, not shown) of red (R)/green (G)/blue (B), and a light shielding layer (BM) 207A that shields the light between adjacent pixels formed therein.
In FIG. 13, the reference symbol 205X schematically shows liquid crystal molecules in the liquid crystal layer 205.
In the opposed substrate 206, a clearance between adjacent light shielding layers (BM) 207A is a pixel opening part 207B.
In the liquid crystal panel 4, the plurality of pixels arranged in matrix are divided into pixels PL that display data for left visual field with respect to the display screen and pixels PR that display data for right visual field with respect to the display screen.
As shown in FIG. 13, when seen in the cross-sectional view, the pixel PL for left visual field and the pixel PR for right visual field are alternately arranged.
For example, seen in a plane view, a pixel group for left visual field in line composed of a plurality of pixels PL for left visual field arranged in line and a pixel group for right visual field in line composed of a plurality of pixels PR for right visual field arranged in line are alternately arranged in stripe.
A parallax barrier layer 208 including a light shielding part 208A and an opening part 208B is formed in a viewing side of the opposed substrate 206.
The position of the pixel opening part 207B formed between adjacent light shielding layers (BM) 207A and the position of the opening part 208B formed in the parallax barrier layer 208 are deviated from each other. Specifically, the opening part 208B of the parallax barrier layer 208 is positioned between the pixel opening part 207B of the pixel PL for left visual field and the pixel opening part 207B of the pixel PR for right visual field that are adjacent to each other.
In the liquid crystal display apparatus 3, display data from the pixel PL for left visual field passes through the pixel opening part 207B of the pixel PL for left visual field and the opening part 208B of the parallax barrier layer 208, and is selectively emitted to the left side with respect to the display screen. Hence, a display image IL for left visual field can be observed by an observer in the left side with respect to the display screen.
Similarly, display data from the pixel PR for right visual field passes through the pixel opening part 207B of the pixel PR for right visual field and the opening part 208B of the parallax barrier layer 208, and is selectively emitted to the right side with respect to the display screen. Hence, a display image IR for right visual field can be observed by an observer in the right side with respect to the display screen.
In the liquid crystal display apparatus 3, the distance between the light shielding layer (BM) 207A and the parallax barrier layer 208, and the opening position and the opening diameter of the pixel opening part 207B and the opening part 208B of the parallax barrier layer 208 are designed so that the plurality of images IL and IR are displayed while being separated in angle as described above.
A liquid crystal display apparatus of parallax barrier system with right and left two screens has a problem of crosstalk, which means the incomplete isolation of the display image IL for left visual field and the display image IR for right visual field so that a part of a display image leaks into the other display image.
In particular, one display image tends to leak into the other display image in the range of the visual angle in the neighborhood of the boundary of two display images. Furthermore, particularly in a display image with much black display, even a small amount of leakage of the other display image tends to be visualized as leaked image.
When the level of crosstalk is high, a part of the display image that should be seen by one observer in one side with respect to the display screen enters the display image that should be seen by the other observer in the other side with respect to the display screen. Thus, display defects occur in which the two display images are overlapped.
The above-stated problem is not limited in the liquid crystal display apparatus with right and left two screens, but the same problem occurs in any liquid crystal display apparatus of parallax barrier system with multi screen.
To address with the problem of crosstalk stated above in which a plurality of display images are mixed in a liquid crystal display apparatus of parallax barrier system with multi screen, patent document 1 discloses a crosstalk correction image generation method to estimate the influence of crosstalk in advance and write the crosstalk corrected potential based on this data into a pixel electrode (see e.g., Claims 1 to 4, and Abstract).
Further, patent document 2 arranges a plurality of parallax barrier layers (33, 36) to reduce crosstalk (see, e.g., Claim 1 and FIG. 1).
However, the method of patent document 1 does not suppress the occurrence of crosstalk itself. It is required in the method of patent document 1 to calculate the correction amount by estimating the crosstalk in advance and to execute the calculated correction amount in a drive circuit, which complicates the circuit configuration.
The method of patent document 2 requires arrangement of a plurality of parallax barrier layers, which increases the cost.
Further, a liquid crystal display apparatus typically has visual angle dependencies, and display properties such as a contrast ratio (CR) are different between a case in which the display screen is seen from the front and a case in which the display screen is seen from a slanted direction. A liquid crystal display apparatus with single screen typically used in TVs or PC monitors has smaller CR with increasing angle from the front with respect to the display screen.
It is not usually assumed that the liquid crystal display apparatus of parallax barrier system with multi screen is used in the frontal visual field. It is usually assumed that the liquid crystal display apparatus is used in the slanted direction. For example, in a liquid crystal display apparatus with right and left two screens, a desired visual field may often be the range in which the visual angle is moved by about 20 to 50° in the left side and the right side from the front.
Accordingly, when the above typical liquid crystal display apparatus with single screen in which the CR decreases in the slanted visual field is directly applied to the liquid crystal display apparatus with multi screen, display properties such as CR and gamma characteristic are degraded since the liquid crystal display apparatus is used with low CR of the liquid crystal display apparatus itself in the slanted visual field, which is supposed to be the main state of usage.
The problem state above that the CR decreases in the slanted visual field can be solved to some extent by using a lateral electric field drive system of IPS (In-Plane Switching) mode or FFS (Fringe Field Switching) mode having the most excellent viewing angle characteristic.
However, when a liquid crystal mode of a lateral electric field drive system in which excellent CR can be obtained in a wide range of visual field is applied to the liquid crystal display apparatus with multi screen, this causes visual fields with degraded display properties due to the crosstalk of a plurality of display images. This is because, when a part of the display image that should be seen by one observer in one side with respect to the display screen enters the display image that should be seen by the other observer in the other side with respect to the display screen, the influence of the mixed display image increases if the luminance level of the display image which should be seen by the observer is low.